Cholesterol and glycolipids self-associate in lipid bilayers to form organized compositional microdomains (Thompson, T. E., et al., Annu. Rev. Biophys. Chem. 14:361 (1985)). Glycosyl-phosphatidylinositol (GPI)-anchored proteins and other lipid-linked proteins may preferentially partition into glycolipid microdomains that are resistant to nonionic detergent solubilization (Schroeder, R., et al., Proc. Natl. Acad. Sci. USA. 91:12130 (1994); Brown, D. A. and Rose, J. K., Cell 68:533 (1992); Letarte-Murhead, M., et al., Biochem. J. 143:51 (1974); Hoessli, D. and Runger-Brandle, E., Exp. Cell. Res. 166:239 (1985); Hooper, N. M. and Turner, A. J., Biochem. J. 250:865 (1968); Sargiacomo, M., et al., J. Cell. Biol. 122:789 (1993); Lisanti, M. P., et al., J. Cell. Biol. 123:595 (1993)). GPI-anchored proteins appear to be sorted into glycolipid, detergent-resistant "rafts" in the trans-Golgi network for polarized delivery to the cell surface by caveolin-rich smooth exocytotic carrier vesicles (Brown, D. A. and Rose, J. K., Cell 68:533 (1992); Sargiacomo, M., et al., J. Cell. Biol. 122:789 (1993); Lisanti, M. P., et al., J. Cell. Biol. 123:595 (1993); Brown, D., et al., Science 245:1499 (1989); Simons, K. and van Meer, G., Biochemistry 27:6197 (1988); Garcia, M., et al., J. Cell Sci. 104:1281 (1993); Kurzchalia, T. V., et al., J. Cell Biol. 118:1003 (1992); Dupree, P., et al., EMBO J. 12:1597 (1993); Hannan, L. A., et al., J. Cell. Biol. 120:353 (1993)). On the cell surface, they are thought to reside in smooth membrane invaginations known as caveolae (Rothberg, K. G., et al., J. Cell. Biol. 110:637 (1990); Ying, Y., et al., Cold Spring Harbor Symp. Quant. Biol. 57:593 (1992); Ryan, U. S., et al., J. Appl. Physiol. 53:914 (1982); Stahl, A. and Mueller, B. M., J. Cell Biol. 129:335 (1995)), which are apparently also rich in glycolipids, cholesterol, and caveolin (Kurzchalia, T. V., et al., J. Cell Biol. 118:1003 (1992); Dupree, P., et al., EMBO J. 12:1597 (1993); Parton, R. G., J. Histochem. Cytochem. 42:155 (1994); Rothberg, K. G., et al., Cell 68:673 (1992); Schnitzer, J. E., et al., Proc. Natl. Acad. Sci. USA 92:1759 (1995); Montessano, R., et al., Nature 296:651 (1982)). Antibody cross-linking of cell surface glycolipids (Thompson, T. E., et al., Annu. Rev. Biophys. Chem. 14:361 (1985)) and GPI-linked proteins (Mayor, S., et al., Science 264:1948 (1994)) can increase sequestration into clusters and induce cell activation (Thompson, T. E., et al., Annu. Rev. Biophys. Chem. 14:361 (1985); Thompson, L. F., et al., J. Immunol. 143:1815 (1969); Korty, P. E., et al., J. Immunol. 146:4092 (1991); Davies, L. S., J. Immunol. 141:2246 (1988)), apparently through lipid-anchored nonreceptor tyrosine kinases (NRTKs) (Stefanova, I., et al., Science 245:1016 (1991); Shenoy-Scaria, A. M., et al., J. Immunol. 149:3535 (1992); Thomas, P. M. and Samelson, L. E., J. Biol. Chem. 267:12317 (1992); Cinek, T. and Horejsi, V., J. Immunol. 149:2262 (1992)). Caveolae have been implicated not only in signaling but also in transport via endocytosis, transcytosis, and potocytosis (Montessano, R., et al., Nature 296:651 (1982); Schnitzer, J. E., Trends. Cardiovasc. Med. 3:124 (1993); Oh, P., et al., J. Cell Biol. 127:1217 (1994); Schnitzer and Oh, P., J. Biol. Chem. 269:6072 (1994); Millci, A. J., et al., J. Cell Biol. 105:2603 (1987); Anderson, R. G. W., et al., Science 265:410 (1992)). Low density, Triton-insoluble membranes are frequently equated with caveolae (Sargiacomo, M., et al., J. Cell. Biol. 122:789 (1993); Lisanti, M. P., et al., J. Cell. Biol. 123:595 (1993); Chang, W.-J., et al., J. Cell. Biol. 126:127 (1994); Lisanti, M. P., et al., J. Cell. Biol. 126:111 (1994)). The physiological functions of, and interrelations between, caveolae, detergent-resistant microdomains, and various lipid-anchored molecules remain undefined.